Currently there is a trend towards making antennas for hand-held radio frequency cellular communication terminals smaller so that they can easily fit within small terminals. Examples of small terminals include flip or slide mobile cellular telephones. However, when an antenna is made smaller the bandwidths associated with its resonances tend to decrease.
Modern mobile cellular communication terminals are typically multi-band terminals and may be multi-mode. A multi-mode terminal is able to operate using one of several different protocols. For example, a multi-mode terminal may be able to transmit/receive using GSM or WCDMA protocols. A multi-band terminal is able to transmit/receive using different licensed frequency bands. The GSM licensed frequency bands are US-GSM (824-894 MHz), E-GSM (880-960 MHz), PCN1800 (1710-1880 MHz), PCS1900 (1850-1990 MHz The WCDMA licensed frequency bands are US-WCDMA1900 (1850-1990); WCDMA21000 (Tx: 1920-1980I Rx: 2110-2180).
Typically an antenna used is a GSM multi-band terminal has two resonances. The bandwidth of the lowest resonance is suitable for covering the US-GSM and/or E-GSM communication bands and the second lowest resonance is suitable for covering the PCN and/or PCS communication bands. The bandwidth of the second lowest resonant mode is not wide enough to cover the WCDMA2100 communication band. Therefore a single small antenna cannot be used in a multi-mode/band terminal to cover the four GSM bands and also the WCDMA2100 band.
It would therefore be desirable to be able to modify an antenna so that one of its resonances is adapted to cover a desired communication band while maintaining acceptable performance of the antenna for other communication bands.
In particular, it would be desirable to be able to modify an antenna so that the bandwidth of its second lowest resonance is increased to cover the WCDMA2100 communication band while also maintaining acceptable performance of the antenna in the GSM communication bands.